what kind of oil do i put on a 2015 subaru imprerzza

Follow the recommendation in the owner's manual. It must have low miles, so I would use 5W-30 or 10W-30. Others may have a different choice.

0W-20 synthetic is what Subaru requires but 5W-20 synthetic should work just fine, this is what I am using in my 2015 Forester.

I strongly prefer the protection of higher viscosity at temperature, so follow Subaru's INTERNATIONAL spec of 5w30 synthetic on ALL motors. The 0w20 US/Canada spec is used only to reduce very cold start timing chain initial chatter...and possibly to squeeze that extra +0.1mpg to maybe take advantage of a small round-up possibility for eco ratings. Since a worrying percentage of these soft-ring modern rings gulp oil, using the sturdier 5w30 spec is a no-brainer to reduce consumption too, as horizontally opposed motors don't rely on splashability of ultra-low viscosity lubes. Mobil1 is on sale for 6qts/$28 at COSTCO every 6 or so weeks, so grab it there and keep the extra qt in your trunk.

Its depend on your environment temperature in either and in summer as by definition of the oil grade standard So if your car in cold environments may reach 0 temp than use 0w20 But your environment in little hot like in gulf area you should use 5w40 or maybe up to 5w50

5w is fine down to -10F. 40w or 50w is overkill except in very hot turbo'd motors or when there's seepage. I LIKE Mobil 0w40 for racing a pressurized motor, but 5w30 is just fine...except if there's seepage, when I go 20w50 summer and 10w40 winter.